Methods for forming a metal contact in a semiconductor device in which an ohmic layer is formed while forming a barrier metal layer

ABSTRACT

A metal contact in a semiconductor device is formed by forming an insulating layer having a contact hole therein on a silicon substrate. A cobalt layer is formed on a bottom and inner walls of the contact hole. A cobalt silicide layer is formed at the bottom of the contact hole while forming a titanium layer on the cobalt layer. A plug is formed on the titanium layer so as to fill the contact hole.

RELATED APPLICATION

This application claims the benefit of and priority to Korean PatentApplication No. 2002-50072, filed Aug. 23, 2002, the disclosure of whichis hereby incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to methods of manufacturing semiconductordevices, and, more particularly, to methods of forming metal contacts insemiconductor devices.

BACKGROUND OF THE INVENTION

As semiconductor devices have become more highly integrated, the designrules for semiconductor devices have been gradually reduced.Accordingly, the areas associated with a contact, which connectsindividual devices to circuit interconnect wiring in the semiconductordevice, and a via contact, which connects an upper interconnect wiringto a lower interconnect wiring, have generally been reduced. Inaddition, contact depth is generally increasing due to a multi-layeredsemiconductor device structure.

Consequently, because the resistance of contacts is generallyincreasing, which may degrade semiconductor device characteristics,technology for reducing contact resistance may be desirable. Withcontact surface area decreasing and depth increasing, achieving adequatestep coverage may be difficult. In other words, the depth of the contactis increased while reducing the area of the contact to increase anaspect ratio so that a process of filling metal in a contact holewithout a void or disconnection may be difficult.

FIGS. 1A and 1B are sectional views illustrating a conventional methodfor forming a metal contact in a semiconductor device. Referring to FIG.1A, an insulating layer 15 having a contact hole 13 is formed on asilicon substrate 11. A titanium layer 17 and a titanium nitride layer19 are sequentially formed in the contact hole 13 and on the insulatinglayer 15 to form a barrier metal layer 21. The titanium layer 17operates as an ohmic layer and the titanium nitride layer 19 operates asa diffusion barrier layer for preventing the diffusion of a tungstenlayer 25 (refer to FIG. 1B), which will be formed in a subsequentprocess, into the silicon substrate 11. The titanium nitride layer 19may also improve the surface adhesion of the tungsten, which will beformed in a subsequent process. A thermal process, such as a rapidthermal processing (RTP) or a rapid thermal annealing (RTA), isperformed on the silicon substrate 11 having the barrier metal layer 21so that a titanium silicide 23 layer is formed.

Referring to FIG. 1B, a tungsten layer 25 is formed on the barrier metallayer 21 in order to fill the contact hole 13. The tungsten layer 25 maybe formed by chemical vapor deposition (CVD), which has generallyeffective gap filling characteristics. Because the tungsten layer 25 isformed using CVD, the contact hole 13 is generally efficiently filledwith the tungsten layer 25.

Because the titanium silicide 23 layer of FIGS. 1A and 1B has arelatively high level of contact resistance in a highly integratedsemiconductor device, however, another material may be substituted forthe titanium silicide layer 23. Accordingly, a method for forming ametal contact in a semiconductor device using cobalt silicide will nowbe discussed.

FIGS. 2A through 2F are sectional views illustrating a conventionalmethod for forming a metal contact in a semiconductor device usingcobalt silicide. Referring to FIG. 2A, an insulating layer 33 having acontact hole 32 is formed on a silicon substrate 31. A cobalt layer 35is formed in the contact hole 32 and on the insulating layer 33 byphysical vapor deposition (PVD). In addition, a titanium nitride layer37 is formed on the cobalt layer 35.

Referring now to FIG. 2B, a first thermal process, such as RTP or RTA,is performed on the silicon substrate 31 on which the cobalt layer 35and the titanium nitride layer 37 are formed to silicidate the siliconsubstrate 31 and to form a CoSi_(x) layer 39 on the bottom of thecontact hole 32.

Referring now to FIG. 2C, the silicon substrate 31, on which theCoSi_(x) layer 39 is formed, is dipped in a sulfuric acid solution tostrip the cobalt layer 35 and the titanium nitride layer 37 from thecontact hole 32 and the insulating layer 33. As a result, the CoSi_(x)layer 39 remains on the bottom of the contact hole 32. Because theCoSi_(x) layer 39 has a relatively high resistance, the CoSi_(x) layer39 may be transformed into a CoSi₂ type cobalt silicide layer byperforming a subsequent thermal process.

Referring now to FIG. 2D, a second thermal process, such as RTP or RTA,is performed on the silicon substrate 31 on which the CoSi_(x) layer 39is formed to silicidate the silicon substrate 31 and to form a cobaltsilicide 41 layer on the bottom of the contact hole 32. Thereafter, thesilicon substrate 31 having the cobalt silicide 41 layer formed thereonis cleaned. Referring now to FIG. 2E, a titanium layer 43 and a titaniumnitride layer 45 are sequentially formed on the top surface of thesilicon substrate 31 having the cobalt silicide 41 layer to form abarrier metal layer 47.

Referring now to FIG. 2F, a tungsten layer 49 for filling the contacthole 32 is formed on the barrier metal layer 47. The tungsten layer 49is formed using CVD, which has generally effective gap fillingcharacteristics. Because the tungsten layer 49 is formed using CVD, thecontact hole 32 is generally efficiently filled with the tungsten layer49.

According to the method described with respect to FIGS. 2A through 2F,because the cobalt silicide layer 41 has a generally lower reactivity todopant than titanium silicide, the cobalt silicide layer 41 can attain alower contact resistance. Unfortunately, forming a metal contact inaccordance with the method of FIGS. 2A through 2F involves performingthermal processes twice and a strip process. In addition, the cobaltlayer 35 is formed using PVD according to the method described withrespect to FIGS. 2A through 2F, which generally provides poorer stepcoverage. Accordingly, the thickness of the cobalt layer 35 is typicallyincreased to obtain a cobalt silicide layer 41 having a proper thicknesson the contact bottom. When such a thick cobalt layer 35 is deposited, astrip process for removing the cobalt layer 35, which remains after asilicidation process, may be necessary. Furthermore, a reinforcedcleaning process is typically performed after the strip processes.

SUMMARY OF THE INVENTION

According to some embodiments of the present invention, a metal contactin a semiconductor device is formed by forming an insulating layerhaving a contact hole therein on a silicon substrate. A cobalt layer isformed on a bottom and inner walls of the contact hole. A cobaltsilicide layer is formed at the bottom of the contact hole while forminga titanium layer on the cobalt layer. A plug is formed on the titaniumlayer so as to fill the contact hole.

In other embodiments, the plug comprises titanium nitride.

In still other embodiments, a titanium nitride layer is formed on thetitanium layer and the plug is formed on the titanium nitride layer soas to fill the contact hole.

In still other embodiments, the titanium nitride layer has a thicknessof about 50 to 500 Å and is formed using chemical vapor deposition (CVD)at a temperature of about 400 to 750° C. In still other embodiments, theplug comprises at least one of tungsten, titanium nitride, aluminum, andtantalum nitride.

In still other embodiments, the cobalt layer, the titanium layer, andthe titanium nitride layer are formed in situ without a vacuum break.

In still other embodiments, the cobalt layer has a thickness of about 5to 200 Å and is formed using one of physical vapor deposition (PVD) andchemical vapor deposition (CVD).

In still other embodiments, the cobalt layer is formed using PVD at atemperature of about 25 to 500° C.

In still other embodiments, the titanium layer has a thickness of about5 to 150 Å and is formed using chemical vapor deposition (CVD) at atemperature of about 400 to 750° C.

In still other embodiments, the substrate and insulating layer arecleaned after forming the insulating layer.

In further embodiments of the present invention, a metal contact in asemiconductor device is formed by forming an insulating layer having acontact hole therein on a silicon substrate. A cobalt layer is formed ona bottom and inner walls of the contact hole. A cobalt silicide layer isformed at the bottom of the contact hole while forming a titaniumnitride layer on the cobalt layer. A plug is formed on the titaniumnitride layer so as to fill the contact hole.

In still further embodiments of the present invention, a metal contactin a semiconductor device is formed by forming an insulating layerhaving a contact hole therein on a silicon substrate. A cobalt layer isformed on a bottom and inner walls of the contact hole. A cobaltsilicide layer is formed at the bottom of the contact hole while forminga plug that fills the contact hole on the cobalt layer.

In still further embodiments of the present invention, a metal contactin a semiconductor device is formed by forming an insulating layerhaving a contact hole therein on a silicon substrate. A titanium layeris formed on a bottom and inner walls of the contact hole. A cobaltlayer is formed on the titanium layer. A complex silicide layer iscomprising titanium silicide and cobalt silicide is formed at the bottomof the contact hole while forming a titanium nitride layer on the cobaltlayer. A plug is formed on the titanium nitride layer so as to fill thecontact hole.

In still further embodiments of the present invention, a metal contactin a semiconductor device is formed by forming an insulating layerhaving a contact hole therein on a silicon substrate. A titanium layeris formed on a bottom and inner walls of the contact hole. A cobaltlayer is formed on the titanium layer. A complex silicide layercomprising titanium silicide and cobalt silicide is formed at the bottomof the contact hole while forming a plug that fills the contact hole onthe cobalt layer.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features of the present invention will be more readily understoodfrom the following detailed description of specific embodiments thereofwhen read in conjunction with the accompanying drawings, in which:

FIGS. 1A and 1B are sectional views illustrating a conventional methodfor forming a metal contact in a semiconductor device;

FIGS. 2A through 2F are sectional views illustrating a conventionalmethod for forming a metal contact in a semiconductor device usingcobalt silicide;

FIGS. 3A through 3D are sectional views that illustrate methods forforming a metal contact in a semiconductor device according to someembodiments of the present invention;

FIG. 4 is a sectional view that illustrates methods for forming a metalcontact in a semiconductor device according to additional embodiments ofthe present invention;

FIGS. 5A through 5C are sectional views that illustrate methods forforming a metal contact in a semiconductor device according toadditional embodiments of the present invention;

FIG. 6 is a sectional view that illustrates methods for forming a metalcontact in a semiconductor device according to additional embodiments ofthe present invention;

FIGS. 7A through 7D are sectional views that illustrate methods forforming a metal contact in a semiconductor device according toadditional embodiments of the present invention;

FIG. 8 is a sectional view that illustrates methods for forming a metalcontact in a semiconductor device according to additional embodiments ofthe present invention;

FIG. 9 is a schematic view illustrating manufacturing equipment used forforming a metal contact in a semiconductor device according to someembodiments of the present invention;

FIG. 10 is a graph that illustrates contact resistances when metalcontacts are formed in semiconductor devices according to conventionalmethods and methods according to various embodiments of the presentinvention; and

FIGS. 11A and 11B are graphs illustrating contact resistances of N⁺contacts and P⁺ contacts versus contact size when a bit line contact isformed in prior art semiconductor devices and semiconductor devicesaccording to embodiments of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawings and will herein be described in detail. Itshould be understood, however, that there is no intent to limit theinvention to the particular forms disclosed, but on the contrary, theinvention is to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention as defined by theclaims. Like numbers refer to like elements throughout the descriptionof the figures. In the figures, the dimensions of layers and regions areexaggerated for clarity. It will also be understood that when anelement, such as a layer, region, or substrate, is referred to as being“on” another element, it can be directly on the other element orintervening elements may be present. In contrast, when an element, suchas a layer, region, or substrate, is referred to as being “directly on”another element, there are no intervening elements present.

FIGS. 3A through 3D are sectional views that illustrate methods forforming a metal contact in a semiconductor device according to someembodiments of the present invention. Referring now to FIG. 3A, aninsulating layer 105 having a contact hole 103 therein is formed on asilicon substrate 101. A cobalt layer 107, which may function as anohmic layer, is formed on the inner walls and the bottom of the contacthole 103 and on the insulating layer 105. The cobalt layer 107 may beformed to a thickness of about 5 to 200 Å. The cobalt layer 107 may beformed using PVD or CVD (hereafter, CVD is referred to as including anatomic layer deposition (ALD) method). When the cobalt layer 107 isformed using PVD, the cobalt layer 107 is deposited at a temperature ofabout 25 to 500° C. In particular embodiments, the cobalt layer 107 isdeposited at a temperature of about 400 to 500° C. when PVD is used toimprove morphology.

Referring now to FIG. 3B, a titanium layer 109 is formed on the cobaltlayer 107 at a temperature of about 400 to 750° C. using CVD. Thetitanium layer 109 may function as an ohmic layer. The titanium layer109 is formed on the cobalt layer 107, which has been formed on theinner walls and the bottom of the contact hole 103 and on the insulatinglayer 105. The titanium layer 109 may be formed to a thickness of about5 to 150 Å. Because the titanium layer 109 is formed at a relativelyhigh temperature, cobalt silicide 111 is formed on the bottom of thecontact hole 103 when forming the titanium layer 109.

Referring now to FIG. 3C, a titanium nitride layer 113 is formed on thecobalt layer 107 and the titanium layer 109 at a temperature of about400 to 750° C. using CVD. The titanium nitride layer 113 may be formedto a thickness greater than 50 Å, for example, about 50 to 500 Å. Thetitanium nitride layer 113 may function as a diffusion barrier layer forpreventing the diffusion of a material, which will be formed as a plug,for example, tungsten. As a result, the cobalt layer 107, the titaniumlayer 109, and the titanium nitride layer 113 may operate as a barriermetal layer 115.

Referring now to FIG. 3D, a plug 117 is formed on the barrier metallayer 115 to fill the contact hole 103 to provide a metal contact. Theplug 117 may comprise a tungsten layer, a titanium nitride layer, analuminum layer, and/or a tantalum nitride layer.

Unlike a conventional method in which two thermal processes and a stripprocess are performed, the cobalt silicide may function as an ohmiclayer by performing relatively simple processing while forming a metalcontact in a semiconductor device in accordance with some embodiments ofthe present invention described above with respect to FIGS. 3A through3D. In addition, in accordance with some embodiments of the presentinvention described above with respect to FIGS. 3A through 3D, thecobalt layer and the titanium layer formed on the bottom of the contacthole may function as an ohmic layer. Accordingly, the thickness of thecobalt layer may be reduced compared to that of conventional methods inwhich only the cobalt layer is used as an ohmic layer. Furthermore, thecobalt silicide is formed when forming the titanium layer at arelatively high temperature, which may allow the thickness of the cobaltlayer to be reduced.

FIG. 4 is a sectional view that illustrates methods for forming a metalcontact in a semiconductor device according to additional embodiments ofthe present invention. The structure and operative effects of the FIG. 4embodiments of the present invention are similar to those of theembodiments described with respect to FIGS. 3A through 3D. In FIG. 4,however, a plug 119 comprises a titanium nitride layer, which is used asa barrier metal layer. More specifically, a metal contact in asemiconductor device is formed as described above with respect to FIGS.3A and 3B. Thereafter, referring to FIG. 4, the plug 119 is formed on atitanium layer 109 to fill a contact hole 103 so that a metal contact iscompleted. The plug 119 may comprise a titanium nitride layer having athickness of about 20 to 3000 Å.

FIGS. 5A through 5C are sectional views that illustrate methods forforming a metal contact in a semiconductor device according toadditional embodiments of the present invention. Referring to FIG. 5A,an insulating layer 205 having a contact hole 203 therein is formed on asilicon substrate 201. A cobalt layer 207, which my function as an ohmiclayer, is formed on the inner walls and the bottom of the contact hole203 and on the insulating layer 205. The cobalt layer 207 may be formedto a thickness of about 5 to 200 Å. The cobalt layer 207 may be formedusing PVD or CVD including ALD. When the cobalt layer 207 is formedusing PVD, the cobalt layer 207 may be deposited at a temperature ofabout 25 to 500° C. In particular embodiments, the cobalt layer 207 isdeposited at a temperature of about 400 to 500° C. when PVD is used toimprove morphology.

Referring now to FIG. 5B, a titanium nitride layer 209 is formed on thecobalt layer 207 at a temperature of about 400 to 750° C. using CVD. Thetitanium nitride layer 209 is formed on the cobalt layer 207, which hasbeen formed on the inner walls and the bottom of the contact hole 203and on the insulating layer 205. The titanium nitride layer 209 may beformed to a thickness greater than 50 Å, for example, about 50 to 150 Å.The titanium nitride layer 209 may function as a diffusion barrier layerfor preventing a material, which will be formed as a plug, for example,tungsten, into a lower silicon layer. Because the titanium nitride layer209 is formed at a relatively high temperature, cobalt silicide 211 isformed on the bottom of the contact hole 203 when forming the titaniumnitride layer 209. Accordingly, the cobalt layer 207 and the titaniumnitride layer 209 may operate as a barrier metal layer.

Referring now to FIG. 5C, a plug 213 is formed on the titanium nitridelayer 209 as the barrier metal layer to fill the contact hole 203 toprovide a metal contact. The plug 213 may comprise a tungsten layer, atitanium nitride layer, an aluminum layer, and/or a tantalum nitridelayer.

Unlike a conventional method in which two thermal processes and a stripprocess are performed, the cobalt silicide may function as an ohmiclayer by performing relatively simple processing while forming a metalcontact in a semiconductor device in accordance with some embodiments ofthe present invention described above with respect to FIGS. 5A through5C.

In addition, in accordance with some embodiments of the presentinvention described above with respect to FIGS. 5A through 5C, thecobalt silicide is formed when the titanium layer is formed at arelatively high temperature. Accordingly, the thickness of the cobaltlayer may be reduced.

FIG. 6 is a sectional view that illustrates methods for forming a metalcontact in a semiconductor device according to additional embodiments ofthe present invention. The structure and operative effects of the FIG. 6embodiments of the present invention are similar to those of theembodiments described with respect to FIGS. 5A through 5C. In FIG. 6,however, a plug 215 comprises a titanium nitride layer, which is used asa barrier metal layer. More specifically, a metal contact in asemiconductor device is formed as described above with respect to FIG.5A. Thereafter, referring now to FIG. 6, the plug 215 is formed on acobalt layer 217 to fill a contact hole 203. The plug 215 may comprise atitanium nitride layer having a thickness of about 20 to 3000 Å. Whenforming the plug 215, cobalt silicide 211 is formed on the bottom of thecontact hole 203.

FIGS. 7A through 7D are sectional views that illustrate methods forforming a metal contact in a semiconductor device according toadditional embodiments of the present invention. Referring now to FIG.7A, an insulating layer 305 having a contact hole 303 therein is formedon a silicon substrate 301. A titanium layer 307, which may function asan ohmic layer, is formed on the inner walls and the bottom of thecontact hole 303 and on the insulating layer 305. The titanium layer 307may have a thickness of about 5 to 150 Å. The titanium layer 307 may beformed using PVD as shown in FIG. 7A. In other embodiments, the titaniumlayer 307 may be formed at a temperature of about 400 to 750° C. usingCVD. When the titanium layer 307 is formed at a temperature using CVD,titanium silicide is formed on the bottom of the contact hole 303, whichis not shown in FIG. 7A.

Referring now to FIG. 7B, a cobalt layer 309, which may function as anohmic layer, is formed on the titanium layer 307. The cobalt layer 309may have a thickness of about 5 to 200 Å. The cobalt layer 309 may beformed using PVD or CVD including ALD. When the cobalt layer 309 isformed using PVD, the cobalt layer 309 is deposited at a temperature ofabout 25 to 500° C. In particular embodiments, the cobalt layer 309 isdeposited at a temperature of about 400 to 500° C. when PVD is used toimprove morphology.

Referring now to FIG. 7C, a titanium nitride layer 311 is formed on thecobalt layer 309 at a temperature of about 400 to 750° C. using CVD. Thetitanium nitride layer 311 is formed on the cobalt layer 309, which hasbeen formed on the inner walls and the bottom of the contact hole 303and on the insulating layer 305. The titanium nitride layer 311 may havea thickness greater than 50 Å, for example, about 50 to 500 Å. Becausethe titanium nitride layer 311 is formed at a relatively hightemperature, complex silicide 313 of titanium silicide and cobaltsilicide is formed on the bottom of the contact hole 303 when formingthe titanium nitride layer 311. The complex silicide 313, the titaniumlayer 307, and the cobalt layer 309 may function as an ohmic layer. Thetitanium nitride layer 311 may function as a diffusion barrier layer forpreventing the diffusion of a material, which will be formed as a plug,for example, tungsten. As a result, the titanium layer 307, the cobaltlayer 309, and the titanium nitride layer 311 may function as a barriermetal layer.

Referring now to FIG. 7D, a plug 315 is formed on the titanium nitridelayer 311 to fill the contact hole 303 so that a metal contact iscompleted. The plug 315 may comprise a tungsten layer, a titaniumnitride layer, an aluminum layer, and/or a tantalum nitride layer.

Unlike a conventional method in which two thermal processes and a stripprocess are performed, the cobalt silicide may function as an ohmiclayer by performing relatively simple processing while forming a metalcontact in a semiconductor device in accordance with some embodiments ofthe present invention described above with respect to FIGS. 7A through7D. In addition, in accordance with some embodiments of the presentinvention described above with respect to FIGS. 7A through 7D, thecobalt layer and the titanium layer formed on the bottom of the contacthole may function as an ohmic layer. Accordingly, the thickness of thecobalt layer may be reduced compared to that of conventional methods inwhich only the cobalt layer is used as an ohmic layer. Furthermore, thecobalt silicide is formed when forming the titanium layer at arelatively high temperature, which may allow the thickness of the cobaltlayer to be reduced.

FIG. 8 is a sectional view that illustrates methods for forming a metalcontact in a semiconductor device according to additional embodiments ofthe present invention. The structure and operative effects of the FIG. 8embodiments of the present invention are similar to those of theembodiments described with respect to FIGS. 7A through 7D. In FIG. 8,however, a plug 317 comprises a titanium nitride layer, which is used asa barrier metal layer. More specifically, a metal contact in asemiconductor device is formed as described above with respect to FIGS.7A and 7B. Thereafter, referring now to FIG. 8, the plug 317 is formedon a cobalt layer 309 to fill a contact hole 303. The plug 317 maycomprise a titanium nitride layer having a thickness of about 20 to 3000Å. When forming the plug 317, cobalt silicide 313 is formed on thebottom of the contact hole 303.

FIG. 9 is a schematic view illustrating manufacturing equipment used forforming a metal contact in a semiconductor device in accordance withsome embodiments of the present invention. More specifically, theequipment according to embodiments of the present invention comprises aplurality of chambers installed on a body 401 and a transfer module 403,which is located in the body 401 for transferring wafers to eachchamber. The chambers installed on the body 401 include a cobaltdeposition chamber 405, a titanium deposition chamber 407, a titaniumnitride deposition chamber 409, a cooling chamber 411, a load lockchamber 413, and a cleaning chamber 415. A wafer loaded in the load lockchamber 413 having an insulating layer with a contact hole formedtherein formed thereon is cleaned in the cleaning chamber 415 and layersare formed on the wafer as it passes through each of the chambers 405,407, and 409. Thereafter, the wafer including the layers is cooled inthe cooling chamber 411. The cooled wafer is then discharged to theoutside via the load lock chamber 413.

According to some embodiments of the present invention, when a metalcontact in a semiconductor device is formed using the above-describedequipment, the depositions of the cobalt layer, the titanium layer, andthe titanium nitride layer, the depositions of the cobalt layer and thetitanium nitride layer, and/or the depositions of the titanium layer,the cobalt layer, and the titanium nitride layer can be performed on thewafer in situ after the wafer is cleaned without a vacuum break.

If the cobalt layer is deposited in cobalt layer deposition equipmentand a titanium layer and a titanium nitride layer are deposited in theother equipment after a vacuum break as in a conventional method,CoO_(x) may be generated on the cobalt layer so that the generation ofan ohmic layer is interrupted and a resistance is increased.Accordingly, a cleaning process may be required after the deposition ofthe cobalt layer. When the equipment of FIG. 9 is used, however, thewafers are cleaned and the cobalt layer, the titanium layer, and thetitanium nitride layer are deposited in situ without a vacuum break sothat the number and the time of processes are reduced while attaining arelatively stable contact resistance.

FIG. 10 is a graph that illustrates contact resistances when metalcontacts are formed in semiconductor devices according to conventionalmethods and methods according to various embodiments of the presentinvention. The horizontal axis denotes experimental conditions and thevertical axis denotes the contact resistance distribution of 1000contacts. More specifically, reference numerals a and a′ denote contactresistances when a cobalt layer is formed to a thickness of 100 Å, atitanium layer is formed to a thickness of 75 Å using CVD, and atitanium nitride layer is formed to a thickness of 250 Å using CVDaccording to the embodiments of FIGS. 3A through 3D. Reference numeralsb and b′ denote contact resistances when the cobalt layer is formed to athickness of 200 Å, the titanium layer is formed to a thickness of 75 Åusing CVD, and the titanium nitride layer is formed to a thickness of250 Å using CVD according to the embodiments of FIGS. 3A through 3D.Reference numerals c and c′ denote contact resistances when the cobaltlayer is formed to a thickness of 100 Å according to the embodiments ofFIGS. 7A through 7D. Reference numerals d and d′ denote contactresistances of conventionally formed cobalt silicide. Reference numeralse, e′, f, and f′ denote contact resistances of conventionally formedtitanium silicide. In addition, reference numerals a, b, c, d, e, and fare the contact resistances when the layers are annealed at atemperature of 750° C. for 30 minutes. Reference numerals a′, b′, c′,d′, e′, and f′ are the contact resistances when the layers are annealedat a temperature of 750° C. for 30 minutes twice.

As shown in FIG. 10, the contact resistance of a semiconductor device,according to embodiments of the present invention, is generally lessthan the contact resistances of conventionally formed titanium silicideand cobalt silicide. In addition, even when the thermal processes areperformed twice, the contact resistance of the semiconductor deviceaccording to embodiments of the present invention is generally less thanthe contact resistances of conventionally formed titanium silicide andcobalt silicide.

FIGS. 11A and 11B are graphs illustrating contact resistances of N⁺contacts and P⁺ contacts versus contact size when a bit line contact isformed in prior art semiconductor devices and semiconductor devicesaccording to embodiments of the present invention. More specifically, inFIGS. 11A and 11B, Co 100A, denoted by transparent rectangles, and Co200A, denoted by transparent circles, are formed by the conditionsdenoted by reference characters a and b of FIG. 10. In other words, Co100A and Co 200A denote the cases where metal contacts are formedaccording to embodiments of the present invention. CiSi₂, denoted bytransparent diamonds, is formed by the conditions denoted by referencecharacter d of FIG. 10. In other words, CiSi₂ denotes the case where acontact is formed by conventional cobalt silicide. TiSi₂, denoted bytransparent inverse triangles, is formed by the conditions denoted byreference characters e or f of FIG. 10. In other words, TiSi₂ denotesthe case where a contact is formed using conventionally formed titaniumsilicide.

As shown in FIGS. 11A and 11B, the contact resistance of the bit linecontact, which is formed according to embodiments of the presentinvention, is less than the contact resistance of the conventional bitline contact where cobalt silicide or titanium silicide is used. Inparticular, the effect is more significant when the contact size isreduced.

Unlike a conventional method in which two thermal processes and a stripprocess are performed, the cobalt silicide may function as an ohmiclayer by performing relatively simple processing while forming a metalcontact in a semiconductor device in accordance with some embodiments ofthe present invention. In addition, in accordance with some embodimentsof the present invention, the cobalt layer and the titanium layer formedon the bottom of the contact hole may function as an ohmic layer.Accordingly, the thickness of the cobalt layer may be reduced comparedto that of conventional methods in which only the cobalt layer is usedas an ohmic layer. Furthermore, the cobalt silicide is formed whenforming the titanium layer at a relatively high temperature, which mayallow the thickness of the cobalt layer to be reduced.

In concluding the detailed description, it should be noted that manyvariations and modifications can be made to the preferred embodimentswithout substantially departing from the principles of the presentinvention. All such variations and modifications are intended to beincluded herein within the scope of the present invention, as set forthin the following claims.

1-26. (canceled)
 27. A method of forming a metal contact in asemiconductor device, comprising: forming an insulating layer having acontact hole therein on a silicon substrate; forming a titanium layer ona bottom and inner walls of the contact hole; forming a cobalt layer onthe titanium layer; forming a complex silicide layer comprising titaniumsilicide and cobalt silicide at the bottom of the contact hole whileforming a titanium nitride layer on the cobalt layer; and forming a plugon the titanium nitride layer so as to fill the contact hole.
 28. Themethod of claim 27, wherein the plug comprises at least one of tungsten,titanium nitride, aluminum, and tantalum nitride.
 29. The method ofclaim 27, wherein the titanium nitride layer has a thickness of about 50to 500 Å.
 30. The method of claim 27, wherein the titanium nitride layeris formed using chemical vapor deposition (CVD) at a temperature ofabout 400 to 750° C.
 31. The method of claim 27, wherein the titaniumlayer, the cobalt layer, and the titanium nitride layer are formed insitu without a vacuum break.
 32. The method of claim 27, wherein thecobalt layer has a thickness of about 5 to 200 Å.
 33. The method ofclaim 27, wherein the cobalt layer is formed using one of physical vapordeposition (PVD) and chemical vapor deposition (CVD).
 34. The method ofclaim 33, wherein the cobalt layer is formed using PVD at a temperatureof about 25 to 500° C.
 35. The method of claim 27, wherein the titaniumlayer has a thickness of about 5 to 150 Å.
 36. The method of claim 27,wherein the titanium layer is formed using chemical vapor deposition(CVD) at a temperature of about 400 to 750° C.
 37. The method of claim27, wherein substrate and insulating layer are cleaned after forming theinsulating layer.
 38. A method of forming a metal contact in asemiconductor device, comprising: forming an insulating layer having acontact hole therein on a silicon substrate; forming a titanium layer ona bottom and inner walls of the contact hole; forming a cobalt layer onthe titanium layer; and forming a complex silicide layer comprisingtitanium silicide and cobalt silicide at the bottom of the contact holewhile forming a plug that fills the contact hole on the cobalt layer.39. The method of claim 38, wherein the plug comprises titanium nitride.40. The method of claim 39, wherein the plug has a thickness of about 20to 3000 Å.
 41. The method of claim 38, wherein the titanium layer, thecobalt layer, and the plug are formed in situ without a vacuum break.